Place the spring onion in a bowl and cover with iced water. Set aside for 10 minutes or until curled. Drain.
Meanwhile, cook the noodles in a large saucepan of boiling water for 4 minutes or until tender. Drain well.
While the noodles are cooking, heat the oil in a wok or large frying pan over medium-high heat. Stir-fry the pumpkin for 6 minutes or until tender. Remove from pan.
Add the chicken to the wok or pan and stirfry, in two batches, for 5 minutes or until chicken is cooked through. Return the chicken and pumpkin to the wok or pan with five spice and mushroom. Stir-fry for 3 minutes or until mushroom is tender. Add the tomatoes, soy sauce, ⅓ cup (80ml) water and noodles and stir-fry for 2 minutes or until heated through.
Sprinkle with cashew, pepitas and spring onion curls. Season with pepper to serve.